Process of purifying graphite.



' of chemistry,

UNITED STATES PATENT OFFICE.

EMIL TEISLER, OF BORSDORF, GERMANY.

PROCESS OF PURIFYING GRAPHITE.

dated June 12, 1900.

Application filed December 8 1899. Serial No. 739,702. No specimens.)

To all whom it may concern:

Be it known that I, EMIL TEI'SLER, doctor a subject of the King ofSaxony, residing at Borsdorf, near Leipsic, in the Kingdom of Saxony,German Empire, have invented an Improved Process of Purifying Graphite,of which the following is a specification.

If fluoric acid be allowed to act on impure graphite, fluorides of themineral impurities contained in the graphite are formed. According toDammer, Handbook of Inorganic Chemistry, Vol.2, page 267, these mineralconstituents consist of silicic acid, alumina, iron,

lime, magnesia, and alkalies. The fluorides formed are partly easilysoluble and partly insoluble or only soluble with diificulty. To thelatter two groups belong the fluorides of lime and magnesia, also thesilicium fluoride of the alkalies. Moreover, fluoride of aluminium onlydissolves in a large excess of acid, and even then often onlyincompletely, as is shown by the existence of alumina in ashes ofgraphite exhausted with fluoric acid. It is possible that in such casesthe aluminium fluoride is combined with the fluorides of the alkaliesinto cryolite, which, as is well known, only dissolves with difficultyin acids. The varying solubility of the oxides of alumina of variousorigins in fluoric acid causes us to form the conclusion that thealumina of graphite ashes has a varying solubility in fluoric acid. Thequantity of the insoluble fluorides is unequal in different substancesand varies from ten to fifty per cent. of the total impuritiesoriginally existing in the graphite. These fluorides are dissolved bybeing decomposed by means of various mineral acids or acid salts. Thusfluoride of aluminium dissolves in hydrochloric and sulphuric acids andsolutions of acid sulphates, fluoride of magnesium, cryolite, andfluo-silicic alkalies in sulphuric acid. In practice, for thepurification of graphite only sulphuric acid and bi-sulphate can comeinto question,beoause of technical and commercial reasons, as lessdifficulties in the way of apparatus have to be overcome, and all wasteproducts may be easily employed or used up in actual working. Itherefore in my application only lay stress on the use of sulphuric acidand acid alkali sulphate for the after treatment of graphitepreliminarily purified by means of fluoric acid. It is also somewhatimmaterial whether I employ dilute sulphuric acid or solutions ofbi-sulphates or concentrated sulphuric acid and deliquescentbi-sulphate. The effect of the treatment is almost the same and is onlyfavorably influenced by the presence of alkaline sulphates, probablyowing to the possibility of the formation of easily-solubledouble salts,such as sulphate of calcium and soda. An excess of the solvent mustexist, and this is already required in order to obtain a good mixture ofthe sulphate with the graphite.

Whether it be betterto employ dilute or concentrated acid depends on thesubsidiary circumstancesfor instance, whether it be desired toimmediately remove the fluoric acid released from out of the reactionmixture or not. In the first case concentrated acid is employed, wherebythe fluorides released immediately escape in a gaseous form, while theyremain dissolved otherwise in the dilute sulphuric acid, and are thenonly expelled therefrom during the concentration. It may appearself-evident that a subsequent treatment of the graphite with sulphuricacid will diminish considerably the amount of ash contained inseveralvarieties of graphite, while the preliminary treatment of thesame g'raphites is almost without effect. If sulphuric acid of 60 Baumbe allowed to act at boiling temperature on burned ferruginous clay,which is composed similarly to the ashes of graphite, hardly two percent. of the substances of the clay is dissolved. By means of fluoricacid, however, over eightyper cent. is immediately dissolved,considerable heat being developed, and by the succeeding furthertreatment with dilute or concentrated sulphuric acid a further fifteenper cent. is dissolved. The chemical constitution of the molecules ofthe clay must first be broken up, and this is elfected most thoroughlyby means of fluoric acid.

The simultaneous treatment of graphite with fluoric and sulphuric acidor with fluorides and sulphuric acid in excess is inadvisable for bothtechnical and practical reasons 'i. .e., for technical reasons becausethere is no cheap material for making vessels which c ithstand thecombined action of dilute fiuoric acid, sulphuric acid, and fluosilicicacid, and for practical reasons because we are forced to employ suchfluorides as yield with sulphuric acid soluble sulphates. The cheapestof these are the alkaline fluorides; but these,with the aid of thefiuo-silicic acid present, form the fiuosilico alkalies, which are sodifficult to dissolve and decompose, and the technical effect of thesame would also thus be less. The result of this explains why I laystress on the subsequent or secondary treatment with sulphuric acid oracid sulphates of graphite previously purified with fiuoric acid.

Having now described my invention, what I desire to secure by LettersPatent of the United States is- 1. The process of purifying graphite,consisting of first treating the graphite with dilute fi uoric acid,then exposing it to the ac-,

tion of sulphuric acid, and finally washing it with water.

2. The process of purifying graphite, c011- sisting of first treating itwith fiuoric acid, then exposing it to the action of sulphuric acid andacid sulphates, and finally washing it with water to remove theresultant salts.

In witness whereof I have hereunto set my hand in presence of twowitnesses.

EMIL TEISLER. v-

WVitnesses:

FRANZ EMIL VELL, RICHARD EMIL IIACHBERG.

